1. Field of the Invention
The present invention relates to a turbo compressor, and more particularly, to a turbo compressor having an improved structure to eliminate a leakage flow between an impeller and a shroud.
2. Description of the Related Art
Generally, a turbo compressor comprises a driving motor, an impeller to be rotated by the driving motor, and a shroud spaced from a blade of the impeller. The turbo compressor sucks and compresses gas such as a refrigerant by a centrifugal force due to rotation of the impeller accommodated in the shroud.
The driving motor comprises a stationary stator mounted in a motor chamber, and a rotor rotatably provided inside the stator. The rotor is integrally connected to the impeller by a rotating shaft, and rotates integrally with the impeller.
FIGS. 1 through 3 are sectional and perspective views illustrating an impeller and a shroud provided in a conventional turbo compressor. As shown therein, the conventional turbo compressor comprises a rotating shaft 105 rotating integrally with a driving motor (not shown), an impeller 140 connected to and rotating with the rotating shaft 105, a shroud 160 shrouding the impeller 140 and spaced from the impeller 140, a gas suction part 145 communicating with a first side of the shroud 160 and through which gas is introduced into the impeller 140, and a diffuser 147 communicating with a second side of the shroud 160 and transforming kinetic energy of the gas drawn by the impeller 140 into compression energy.
The impeller 140 comprises an impeller body 141 connected to the rotating shaft 105, and a plurality of blades 143 formed on the impeller body 141 and spaced from the shroud 160.
With respect to a diffusing flow “c” from the gas suction part 145 to the diffuser 147, a gas backflow from the diffuser 147 to the gas suction part 145 is generated through a space 165 because pressure in the gas suction part 145 is relatively low as compared with the pressure in the diffuser 147. Therefore, the shroud 160 is provided with a plurality of backflow prevention grooves 161 to prevent the gas backflow.
The plurality of backflow prevention grooves 161 are annularly provided on the inside circumferential surface of the shroud 160 along a rotating direction of the impeller 140, and are spaced from each other. That is, the backflow prevention grooves 161 are formed as annular grooves having different diameters from each other, and are formed on the inside circumferential surface of the shroud 160, being centered on a rotating axis of the impeller 140.
Thus, the conventional turbo compressor is provided with the plurality of the backflow prevention grooves 161 on the shroud 160, so that the backflow prevention grooves 161 accommodate the gas flowing from the diffuser 147 to the gas suction part 145 along the inside circumference surface of the shroud 160 to prevent the backflow “a” as shown in FIG. 1.
Further, as shown in FIG. 3, velocity and friction of the drawn gas are different according to the rotating direction of the impeller 140 and a shape of a passage between the blades 143, and therefore the velocity difference and the friction difference cause pressures to be differently applied to opposite sides of each blade 143. Such pressure difference in the opposite sides of each blade 143 causes a leakage flow “b”, from a first side of the blade 143 to a second side of the blade 143 across the blade 143, to be generated through the space 165 between the shroud 160 and the blade 143. Also, the leakage flow “b” flows over the adjacent blade 143 across the diffusing flow “c” and affects the diffusing flow “c”. The leakage flow thereby decreases compression efficiency.
However, in the conventional turbo compressor, the plurality of backflow prevention grooves are provided in the shroud in order to eliminate the backflow from the diffuser to the gas suction part, but there is nothing to eliminate the leakage flow, so that the compression efficiency is decreased. That is, because the leakage flow flows along the rotating direction of the impeller, the backflow prevention grooves formed along the rotating direction of the impeller cannot eliminate the leakage flow. Accordingly, to increase the compression efficiency, there is needed to eliminate both the backflow and the leakage flow.